1. Field of the Invention
The present invention relates to in vivo bone transport and lengthening. More particularly, the present invention relates to a flexible cable drive system for in vivo bone transport and lengthening and force transmission to bone tissue that allows clinically convenient placement of a driver and exit portal, and which does not significantly hinder the patient's normal activities.
2. General Background
Intercalary defects in long bones may occur as a result of trauma or after the resection of tumors or infection. With appropriate mechanical fixation, these defects may be managed by autogenous bone grafting, segmental allograft reconstruction, or reconstruction using endoprostheses. Autogenous bone grafting has the disadvantage of donor site morbidity including pain, increased blood loss, and surgical scarring. Furthermore, in the case of large defects it may be difficult or impossible to obtain an optimal volume of autogenous bone. While allografting eliminates the problem of adequate quantity, the incidence of complications such as infection, fracture, and non-union is increased. The risk of exposure to HIV or hepatitis is another concern.
In 1954 Ilizarov reported that mature bone can be elongated by gradual distraction of a fracture callus and called this process distraction osteogenesis. The application of this technique in the form of bone segment transport can obviate the need for open bone grafting in many large diaphyseal defects. However, transfixing wires used in this technique can cause significant complications including wire site infection, pain, and restricted joint motion due to the transfixation of tendons and muscles. These complications are particularly relevant when the Ilizarov device is applied to the femur.
In 1990 Brunner reported that distraction osteogenesis was achievable using intramedullary fixation in sheep tibiae. Brunner's method still relied on the use of an external fixator to provide the force necessary for bone transport. Brunner's work implied that transfixing wires used for internal fixation could potentially be eliminated.
Betz described the use of a telescoping intramedullary rod for distraction osteogenesis. With the Betz device, the patient apparently turned a small knob that protruded from the patient's hip in order to telescopically move the parts relative to one another.
Various patents have issued for implantable distractor devices. Further, certain devices have been published in the literature as published patent applications for example.
An example of a medullary nail is seen in PCT Application No. WO 91/00065 naming Rainer Baumgart and Augustin Betz as applicants. The Betz device describes an intramedullary nail that has a cavity in which an inner part can slide longitudinally without being able to rotate. The wall of the medullary nail which forms the cavity is traversed on both sides by an elongated hole in the region of the driving-in end. At least one fastening hole aligned flush with the elongated hole is provided in the inner part. When the connecting screws are driven into the spaced fastening holes an osteotomy is located between the connecting screws, the edges of the osteotomy are moved apart as the inner part slides longitudinally, and the slowly widening gap between the edges of the osteotomy becomes filled with bone tissue.
An extension apparatus, especially for osteotomic surgery is the subject of U.S. Pat. No. 3,976,060 issued to Hildebrandt et al. The Hildebrandt patent describes a bone extension device that is movably supported in an elongated, slender housing. The extension device includes an extension member movably extending out of a housing. A drive is supported within the housing and operatively connected to the extension device. A drive is energized through a source of power which may be either located in the housing itself or it may be an external power source such as a magnetic field. The power source is operatively connected to the drive. A control is supported within the housing to operate the drive through the power source for moving the extension member. A seal is provided to seal the housing so as to provide a surgically implantable structural unit. The power source can be an electric motor and powered by a battery. Reduction gears are disclosed as rotating a threaded spindle which operates a push rod.
U.S. Pat. No. 4,1577,715 entitled "Intracorporal Drive to Produce a Continuous Traction or Pressure and Method of Operating Same" was issued to Erhardt Westerhoff. The drive provides an extension unit for extension osteotomy and for a compression unit for pressure osteosynthesis, wherein the driving power is generated by the osmotic pressure between two differentially concentrated solutions separated from each other by a semipermeable diaphragm or membrane. The solution of low concentration can also be substituted by pure solvent.
The Grammont et al. U.S. Pat. No. 5,074,882 provides a device that includes a nail for gradually lengthening long bones. The apparatus includes outer and inner sliding tubes connected with a double ratchet mechanism. The nail is fixed by its two extremities in the bone and the device is entirely included within the concerned bone, being lengthened post-operatively by maneuvers applied to the patient's limb. Rotation of a distal part of the limb with respect to the proximal part of the limb allows rotation of the ratchet mechanism with lengthening of the device in one direction, and keeping of the gained length in the other direction while returning the neutral axis of the rotation of the device, thereby featuring a dynamization system, and a system, to limit the range of rotation of the device.
The linear implantable distractors of the prior art suffer because of a failure to afford an easy way of operating such an implantable distraction apparatus, with improved patient comfort, and without bacteriological infiltration.
Various devices have been patented for distractors that are placed externally of the patient's limb. These are referred to often as "Ilizarov-type" distractors, after the Russian inventor Gavriil Ilizarov. As an example, U.S. Pat. No. 4,615,338 entitled "Automatic Compression-Distraction Apparatus" names Gavriil Ilizarov and others as inventors. The '338 patent relates to a drive of a compression-distraction apparatus, comprising a lead screw whose thread is mated with an opening of a ratchet wheel placed in a housing, a pawl interacting with teeth of the wheel and connected to a load bearing element manufactured from an alloy possession plastic memory. The load bearing element has a rectilinear shape and is essentially a tie rod whose one end is rigidly secured to the housing while the other end is coupled to a resilient member and the pawl, with the load bearing element being further provided with an electric heater connected to the housing. Another external compression distraction apparatus is the subject of U.S. Pat. No. 4,973,331 issued to Pursley et al. and entitled "Automatic Compression-Distraction, Torsion Method and Apparatus".